The present invention relates to devices and methods employing microwaves.
Microwave ovens are well-known. They consist of a metal enclosure and a source of microwaves, sometimes referred to as "magnetron." A product to be heated or melted is placed in a non-conductive dielectric receptacle within enclosure. The product-receiving receptacle in the metal enclosure must not be metal.
Industries which employ organic materials, in particular the plastic industry, frequently have to melt organic products which are packed in metal containers. This is true, for instance, in the technique for manufacturing polyurethanes. In that case, prepolymers which are delivered in solid form in metal drums are polymerized. It is then necessary to reheat these products in order to melt them, but this heating must be carried out cautiously because if the temperature of the prepolymers exceeds a given value, for instance 75.degree. C., for too long a time, these products are degraded, with the formation of, for instance, allophanates which it is necessary to avoid. One is therefore compelled to effect a progressive, limited heating.
This heating can be carried out in a stove but the heating time is very long, for instance about 72 hours for a 200 liter drum. Furthermore, the expenditure of energy is very substantial.